package com.wangshuqi.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/*
 * 验证码
 * */
public class VerificationCodeServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器5秒自动刷新一次;
        resp.setHeader("refresh", "5");
        System.out.println("--------------------------------------------");
        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);
        //得到图片
        Graphics2D g = (Graphics2D) image.getGraphics(); //笔
        //设置图片的背景颜色
        g.setColor(Color.white);
        g.fillRect(0, 0, 80, 20);
        //给图片写数据
        g.setColor(Color.BLUE);
        g.setFont(new Font(null, Font.BOLD, 20));
        g.drawString(makeNum(), 0, 20);

        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        // Cache-Control:no-cache ：HTTP/1.1 协议中使用，强制每次请求直接发送给源服务器，而不经过本地缓存版本的校验
        // 建议使用这个
        resp.setHeader("Cache-Control", "no-cache");
        // Pragma:no-cache 和 Cache-Control:no-cache 二选一即可，它只能在 HTTP/1.0 协议下兼容
        // 通常要配合Expires置为0来达到目的
        // resp.setDateHeader("expires", -1);
//        resp.setHeader("Pragma", "no-cache");

        //把图片写给浏览器
        ImageIO.write(image, "jpg", resp.getOutputStream());
    }

    //生成随机数
    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(9999999) + "";
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < 7 - num.length(); i++) {
            sb.append("0");
        }
        num = sb.toString() + num;
        return num;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    }
}
